1. Field of the Invention
The present invention relates to, for example, a coordinate detection system that detects a coordinate indicated on a board face by a pointer or a finger.
2. Description of the Related Art
As one coordinate input unit used for an electronic copyboard, a method of triangulation using an interruption of an infrared ray is known. In the method of triangulation using the interruption of the infrared ray, it is unnecessary to prepare a display, on which a touch panel is installed, and an arbitrarily selected wall can be used as a screen for drawing, for example. For example, when a whiteboard is used as a screen, the coordinate of a pointer shaped like a pen, which is grasped by a user for handwriting, is acquired.
However, in a case where a user handwrites characters or the like on a board face, there is a case where a part of a hand carelessly touches the board face. In the method of triangulation using the interruption of the infrared ray, the light is interrupted to detect the coordinate. Therefore, in a case where the hand grasping the pointer touches the board face, both the pointer and the hand are detected as an interrupting object. Therefore, there may be a case where the coordinate of the pointer cannot be correctly detected.
As one measure of solving this inconvenience, Japanese Laid-open Patent Publication No. 2005-31755 discloses that a switch that is turned on when writing pressure is applied is installed at a tip end of the pointer, it is distinguished whether the hand or the pointer interrupts the light depending on whether the switch is turned on or off when the light is interrupted, and the coordinate of the tip end of the pointer is detected when the switch is turned on.
Further, Japanese Patent No. 4112878 discloses a technique of detecting the coordinate of the pointer without using the interruption of the infrared ray in order to prevent the finger from being detected as the interrupting object. According to Japanese Patent No. 4112878, the coordinate is detected by installing the light source on the tip end of the pointer, and the finger is prevented from being detected as the interrupting object.
However, if a special pointer is necessary as disclosed in Japanese Laid-open Patent Publication No. 2005-31755 or Japanese Patent No. 4112878, in a case where the special pointer does not exist or the special pointer is out of order, there is a problem that the electronic copyboard cannot be used. Further, according to Japanese Laid-open Patent Publication No. 2005-31755, a pen signal receiving part of receiving a signal indicative of whether the switch is turned on or off from the pointer is necessary on a side of a control part. Therefore, there is a problem that the structure becomes complicated and the manufacturing cost increases more.